1. Field of the Invention
This invention pertains to the field of electrical testing equipment. More particularly, this invention pertains to the field of electrical testing equipment which is used for monitoring and recording the operation and/or performance of electrical relays.
2. Description of Related Art
Various devices have been proposed for testing the operation of electrical relays, as disclosed, for example, in U.S. Pat. Nos. 4,319,193, 4,464,628, and 4,961,051. However, because none of these devices has received wide-spread commercial acceptance, relay testing remains, for the most part, a time consuming and inexact process.
Conventionally, testing of electrical relays is accomplished with devices incorporating an analog meter. Specifically, to test a relay, a source of variable power is connected across the coil of the relay and the source voltage is increased gradually. The analog meter is used to give an indication of the amount of current passing through the coil. When sufficient current is supplied to the coil, the electromagnetic field created by the coil causes the armature of the relay to shift or "pickup" from its original position, thereby closing the relay switch, as is conventional.
Prior to the closing of the relay switch, the gradual increase in the source voltage causes a corresponding gradual rise in the position of the needle of the analog meter. However, as the relay switch closes, the movement of the armature through the coil causes an inductive "spike" which appears on the analog meter as a slight jump. The position of this slight jump on the meter scale is estimated by the operator performing the relay test and gives an indication of the pickup voltage or current necessary to activate the relay switch.
After the pickup voltage or current has been determined and recorded, the power of the power source is then gradually decreased. As the power is decreased, the electromagnetic field created by the current passing through the coil decreases sufficiently to allow the armature to shift or "drop away" back to its original position, thereby causing the relay switch to open. The shifting of the armature as the relay switch opens causes a second "spike" which again appears on the analog meter as a slight jump by the needle on the meter scale. The position on the meter scale of the this second slight jump is again estimated and recorded as an indication of the drop away voltage or current. All in all, the conventional relay testing procedure requires several minutes to complete.
As is readily apparent, the results of this testing procedure may often be characterized by significant degrees of error. In addition to the normal instrument error of the analog meter, estimation and interpretation by the operator of the slight needle jumps may give rise to significant errors. Moreover, the apparent position of the slight needle jumps will often be dependent on the speed at which the source voltage of the power source is increased or decreased. Considering the serious implications which erroneous or inaccurate relay testing procedures might bring, for example, in the railroad signal industry, it would be most desireable to eliminate these and other sources of relay testing errors.